In an optical transmission system, signal light transmitted from an optical transmitter is transmitted through an optical transmission line constituted mainly by optical fibers. Then, the signal light arrives at an optical receiver and is received by that optical receiver. In such an optical transmission system, it is required that the optical characteristics of the optical transmission line laid between the optical transmitter and optical receiver be excellent in order to transmit mass information at high speed.
For example, in order to suppress the deterioration of signal light waveform caused by accumulated chromatic dispersion, in an optical transmission line formed by connecting an optical fiber for transmission with a dispersion compensation fiber, the absolute value of the accumulated chromatic dispersion in the overall optical transmission line is controlled smaller. On the other hand, in order to compensate for the loss of signal light suffered during the propagation in the optical fiber for transmission, in the optical transmission line formed by connecting the transmission optical fiber and an amplification optical fiber, the signal light is amplified in the amplification optical fiber. In addition, there are some cases that the foregoing dispersion compensating fiber and the amplification optical fiber are laid in a repeating section, while there are some cases to be installed in repeater stations and so on as a module rolled in a coil form.
Also, when an optical transmission line is changed or extended, there are some cases that another optical fiber is further connected to existing optical fibers.
In the optical transmission line thus formed by connecting a plurality of optical fibers, excellent optical characteristics of the overall optical transmission line are not only required, but also the small loss (connection loss) of a connecting point between the optical fibers constructing the optical transmission line is required. It is noted that the connection loss can be determined by an OTDR (Optical Time Domain Reflectometer) test.
In the OTDR test, a pulse test light is incident from one end of an optical transmission line, and a rear scattering light generated at each position while the pulse test light propagates through the optical transmission line is detected at the one end. Then, based on the time variation of the intensity of the rear scattering light, the distribution of the loss in the longitudinal direction of the optical transmission line will be obtained.
In this way, when the two optical fibers are connected with each other, the intensities of the scattering light at the front and rear of the connecting point are measured by the OTDR test. Then, a small difference between these intensities of the scattering light is judged a favorable connecting work. On the other hand, the large difference between these intensities of the scattering light is judged a failed connecting work, resulting in making the connecting work again.
Non-Patent Document 1: OFS, “Mixing TrueWaveR RS Fiber with Other Single-Mode Fiber Designs Within a Network,” (retrieval on Feb. 27, 2004), available at the website of OFS Laboratories, Georgia.